I have a similar set, red piped with pink numerals. In 1937 the HJ straps began to reflect the assignment of the member by using the colors we are familiar with now to denote different specialties according to the NSDAP organisation book 3rd edition. I know that red piped straps without numerals were sold by RZM stores at one time. It's possible that these straps were sold without numbering and the numbers were added sometime in 1937 prior to the introduction of the new pattern straps in September of 1938. Here is a scan of my straps, very similar to the set you've just picked up on EbayDE.